Process for making fatty peracids



United States PROCESS FOR MAKING FATTY PERACIDS Daniel Swern and Winfred E. Parker, Philadelphia, Pa., assignors to the United States of America as represented by the Secretary of Agriculture No Drawing. Application September 2, 1954, Serial No. 453,972

invention herein described, for all governmental purposes, throughout the world, with power to grant sublicenses for such purposes, is hereby granted to the Government of the l United States of America.

This invention relates 1.0 the production of fatty peracids.

atent C The fatty peracids as a class are well known and are of great interest and utility because of their versatility and reactivity. Their high oxidizing potential makes them invaluable for converting olefins to epoxides, sulfides to sulfoxides and sulfones, and for many other oxidation reactions. Their use as initiators for free-radical type reactions, particularly vinyl type polymerizations, is another well known application. For this latter use, the progressive change in potency and in rate of decomposition at a given temperature, as the length of the hydrocarbon chain of the peracid increases, gives the operator wide latitude within which to conduct the polymerization, and thus permits control of the rate of polymerization and the molecular weight of the polymer produced. Despite this recognized need for a wide variety of fatty peracids, most of the common fatty acids (C1C1s) have never been described and only a few of the lower members of the series are readily available.

Accordingly, it is an object of this invention to provide a simple and economical process for the production of fatty peracids that is of general applicability and that is especially suitable for making the higher fatty peracids, that is, those containing up to 18 carbon atoms.

The lower fatty peracids, that is, those containing up to 4 carbon atoms, are water soluble and are readily made by treating the fatty acid with aqueous hydrogen peroxide. The reaction is hastened by use of a mineral acid catalyst and approaches an equilibrium:

Because of the reversibility of this reaction, complete conversion of the fatty acid in a practical manner is impossible and it is necessary to use a great excess of hydrogen peroxide in order to achieve a reasonably high conversion. Because the above reaction is carried out in an aqueous system, it is not applicable to the higher fatty acids because their extremely hydrophobic nature prevents reaction.

Various schemes have been proposed for making the higher peracids by use of inert organic solvents and by first converting the fatty acid to the anhydride or acid chloride. These expedients are cumbersome and expensive, and consequently have not been widely used.

We have now discovered a simple, inexpensive, onestep process for converting a fatty compound selected from the group consisting of the saturated fatty acids having from 2 to 18 carbon atoms, the methyl esters of the saturated fatty acids having from 2 to 24 carbon atoms, and mixtures thereof, directly into the peracids with high conversion, without use of organic solvent and without the intermediate formation of the acid anhydride or chloride.

Patented Nov. 19, 1957 According to the invention, the fatty compound is mixed with, that is, suspended or dissolved in at least a molar equivalent of concentrated sulfuric acid, and then, while maintaining the temperature of the mixed acids below that at which significant decomposition of the resulting peracid occurs, that is, below about 40 C., mixing aqueous hydrogen peroxide of about from 30% to 65% concentration with the mixed acids to react the fatty acid with the hydrogen peroxide to produce the corresponding fatty peracid which is thereafter isolated. The sulfuric acid acts both as a catalyst and as a mutual solvent for the reagents. In addition, it acts as a dehydrating agent, thus eifectively removing the water present from the field of reaction. The fatty acids of short or intermediate chain length are readily soluble in the sulfuric acid and the ,,reaction mixture is homogeneous. The higher fatty acids containing up to 18 carbon atoms are sufliciently soluble though the amount of sulfuric acid used need not be sufficient to dissolve completely the fatty acid. It is necessary to use only enough sulfuric acid to make a pasty suspension that can be effectively stirred. The reaction is strongly exothermic and effective cooling is required. Hence it is essential that the reaction mixture be continuously stirred to promote heat transfer and avoid hot spots. The maximum permissible temperature is that at which there is appreciable decomposition of peracid. The lower fatty peracids are less stable than the higher ones. Thus in making peracetic acid it is advisable to keep the temperature below 20 C. while in making perstearic acid, it may be allowed to go as high as about 40 C. without excessive decomposition.

The amount of sulfuric acid required depends on its dual function as (1) solvent or liquefying agent and (2) sequestering agent for the water present.

When making the higher peracids, the first factor is controlling; that. is, enough acid must be used to permit etficient stirring and heat transfer. When the lower peracids are being produced, the second factor is controlling; that is, enough acid must be used to take up the water present in the reagents and also that formed in the reaction without excessive dilution of the sulfuric acid. We have found that the conversion suffers when the sulfuric acid concentration after the reactants are mixed is below about 6070%. Thus, it is clear that it is advantageous to start with concentrated acid (-100%) or even with oleum, in order to minimize the quantity of sulfuric acid used in the process. The molar ratio of sulfuric to fatty acid should be at least 1:1 and is usually in the range of 2-4 to l.

The hydrogen peroxide used may vary in concentration, though we prefer to use the 50% grade. The lower concentrations, down to about 30% may be used but give lower conversions because of the large amount of water in the reagent. Higher concentrations give higher conversions and require the presence of less sulfuric acid but may introduce an explosion hazard if above about 65 The amount of peroxide used in the reaction may likewise be varied widely but we prefer to use a molar ratio of peroxide to fatty acid in the range of about 1.0-1.5 to 1. By use of lower ratios more complete use is made of the peroxide, but only at the expense of lower conversions of the fatty acid. Conversely, higher ratios give high conversions of the fatty acid but low utilization of the peroxide.

In general, our preferred procedure is to dissolve or suspend the fatty acid in the sulfuric acid, cool to about 10 C., add the peroxide slowly with eflicient cooling and stirring while keeping the temperature belowabout 30 0., let stand at room temperature for 1-2 hours, dilute with a large volume of cold water, and recrystallize the thus precipitated crude peracid from a suitable solvent, such as petroleum ether or ordinary ether. Residual fatty acid is easily separated from peracicl by crystallization of the crude product from petroleum ether, since, in ene al a ty a id s m re so ble than he pe a When working with the lower members of the series, P r fi ation m y l be e e t d by a n l vacuum 4 4 ture of perpalmitic and perstearic-acids. Fatty acids from such fats as tallow, soybean oil,. c1ottonsecd oil and lard are also suitable for conversion to mixed peracids after being suitably hydrogenated. Although the examples cited deal with the preparation of individual peracids from pure fatty acids, mixtures of saturated fatty acids, whatever the source, work equally well.

TABLE II Properties of pure fqtt y peracids Ieroxide (28-11103? Hydrogetn,

oxygen percen percen Acid M.P., percent Gal 9949. 9- F u d lc- Fou Percapryllc 31 9. 98 9. 82 59. 5 58,9 10,. l 10. 2 Perpelargonic.---- 35 9. 18 9. 18 62. D 61. 4 10. 4 10. 7 Percaprlc 41 8. 50 8. 52 63. 8 64. l0. 7 10. B erlauric- 52 7. 40 7. 50 56. 7 66. 6 ll. 1 ll. 0 Permyrlstlc- 57 6. 54 6. 56 68. B 68.6 11. 11.4 Perpalmitie.-- 61 5. 87 5. 86 70 5 69. 7 11. 8 11. 6

distillation. many uses when the conversion is above 90%.

By use of the above-described general procedure, we have carried out the experiments summarized in Table I. In each example, ordinary 95% sulfuric acid and 50% Furthermore, purification is unnecessary for 25 We claim;

1. The process for making fatty peracids comprising mixing a a y o po nd s ect d fr m th oup on: sisting of saturated fatty acids having from 2 to 18 carbon atoms, yl esters sa ated att ci s having rom hydrogen peroxide were used. an 2 to 24 carbon atoms, and IIILXHJES thereof, w th at least TABLE I Preparqtzon of fatty peraczds Rcactants, Mols. Reaction Product conditions Example No. Acid used Conversion,

ma x. percent based Peroxide Purity Acid E101 E 50; time, tcmp., on- 01 perof crude min. G'. cent pcracid, percent Acid H20:

1 Lam-town) 0.05 0.10 0.23 30 30 9s 49 7.23 as 2 do .10 .105 15 00 a0 81 77 5.02 81 a 10 079 4e 50 30 so 76 4. 45 e0 4 10 105 4e 10 30 55 04 4. 92 55 5 10 105 is 150 a0 81 77 e. 02 21 0 10 .30 50 05 04 a. 19 95 7 10 15 50 120 so 85 57 5. 59 85 8 10 15 e0 50 a0 53 42 4. e3 9 10 20 60 120 30 85 57 5. 59 a5 10 15 77 120 01 41 a. 60 51 do .10 .15 .77 300 30 57 45 3. 94 07 Stearic (C15) 07 105 60 120 37 e0 44 a. 51 66 Caprylie (Cs) 15 225 32 e0 30 95 e4 9. 44 95 Pelargonic (0100--- .15 .225 .39 c0 30 99 65 9.10 99 Substantially identical results were obtained when the 55 a molar equivalent of concentrated sulfuric acid, then,

methyl esters were used instead of the fatty acids of 2 to 16 carbon atoms. Methyl stearate gave significantly higher yields of peracid than did stearic acid, however, presumably because of its greater solubility in sulfuric acid. While it is not practical (because of low solubility) to use the free fatty acids having more than 18 carbon atoms in our process, the corresponding methyl esters may be used with good results up to at least the saturated C 4 acids. Thus the methyl esters of completely hydrogenated fish oil acids are particularly suitable for use in the process.

Many of the higher fatty peracids have not been previously made or described. Hence, in Table II we have listed some of the properties of the pure compounds that have not previously been described.

Saturated fatty acids of commerce are frequently mixtures of homologous compounds. Thus, commercial stearic acid, which may contain about 50 parts each of stearic and palmitic acids and minor amounts of other fatty acids, can also be used in our process to yield a mix while maintaining the temperature of the mixture of the fatty compound and the sulfuric acid below about 40 C., mixing hydrogen peroxide of about from 30% to 65% concentration with the said mixture of the fatty compound and the sulfuric acid to react the said fatty compound with the hydrogen peroxide to produce the corresponding fatty peracid, and isolating the peracid from the reaction mixture.

2. The process of claim 1 wherein the fatty compound is a saturated fatty acid having from 2 to 18 carbon atoms.

3. The process of claim 1 wherein the fatty compound is the methyl ester of a saturated fatty acid having from 2 to 24 carbon atoms.

4. The process of claim 2 wherein the saturated fatty acid is pelargonic acid.

5 7. The process of claim 2 wherein the saturated fatty OTHER REFERENCES acld steam acld- DAns et a1.: Ber. Deut Chem. 45, 1845-1853 (1912). 8. The process of claim 3 whereln the methyl ester of Erlenmeyer: Helvetica Chemica Acta 8 (1925), the saturated fatty acid is methyl stearate. 792497 5 it a, References Cited in the file of this patent Swem' Chem Revlews 45 (1949) 1 UNITED STATES PATENTS 2,490,800 Greenspan Dec. 13, 1949 

1. THE PROCESS FOR MAKING FATTY PERACIDS COMPRISING MIXING A FATTY COMPOUND SELECTED FROM THE GROUP CONSISTING OF SATURATED FATTY ACIDS HAVING FROM 2 TO 18 CARBON ATOMS, METHYL ESTERS OF SATURATED FATTY ACIDS HAVING FROM 2 TO 24 CARBON ATOMS, AND MIXTURES THEREOF, WITH AT LEAST A MOLAR EQUIVALENT OF CONCENTRATED SULFURIC ACID, THEN, WHILE MAINTAINING THE TEMPERATURE OF THE MIXTURE OF THE FATTY COMPOUND AND THE SULFURIC ACID BELOW ABOUT 40*C., MIXING HYDROGEN PEROXIDE OF ABOUT FROM 30% TO 65% CONCENTRATION WITH THE SAID MIXTURE OF THE FATTY COMPOUND AND THE SULFURIC ACID TO REACT THE SAID FATTY COMPOUND WITH THE HYDROGEN PEROXIDE TO PRODUCE THE CORRESPONDING FATTY PERACID, AND ISOLATING THE PERACID FROM THE REACTION MIXTURE. 